FEELIN' CRABBY?Too many restaurants use too much filler and not enough crab, then fry the thing to death and smother its flavor with a heavy sauce. The best crab cakes are nothing but big chunks of lump meat from a blue crab (or maybe Dungeness crab on the Pacific Coast) bound with little more than egg, mayonnaise, and a pinch of breadcrumbs. They are then quickly sautéed in butter and served with pan juices or a squirt of lemon and some tartar sauce. Done this way, crab cakes are among the purest, sweetest items in the American pantheon of great dishes. That’s the way chef Ed Brown does it at New York’s The SeaGrill (19 W. 49th St.; 212-332-7610), set right on Rockefeller Center’s skating rink.